To the casual observer, the city of Mont Belvieu, Texas, is just another oil rig-spotted town on the Gulf Coast. But thanks to an enormous salt-cavern gas storage facility directly beneath it, it is famous for defining the price for propane.

If you use propane, chances are the fuel you’re using has spent some quality time in the caverns under Mont Belvieu. Back in 1955, the Warren Petroleum Company built the facility to hold some of the gas they had captured during the oil drilling process. They built 26 storage caverns in all, with a storage capacity of 43 million barrels of propane, butane, ethane, and natural gas. Several other similar facilities have been built in the area since. Today it is the largest gas liquids storage facility in the United States, with only one other similar facility located in Conway, Kansas.

With the nearly limitless amount of propane storage beneath it, Mont Belvieu has become synonymous with US propane prices. When you check for the ‘spot’ price, you’ll see it defined as the ‘Mont Belvieu’ price.

But this fame hasn’t gone to the heads of Mont Belvieu residents, of which there is only about 2,300 total. Life is pretty simple in this quiet town, but it is a simplicity that belies enormous economic importance to propane companies and consumers everywhere.